Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge devices are used to control the wing coefficient of lift. The leading edge device is known as a slat. On larger aircraft there may be several slats spaced along the wing edge. During normal flight the slats are retracted against the leading edge of the wing. However, during take-off and landing they are deployed forwardly of the wing so as to vary the airflow across and under the wing surfaces. The slats usually follow an arcuate or curved path between their stowed and deployed positions. By varying the extent to which the slat is deployed along said path, the lift provided by the wing can be controlled.
An assembly is required to support and guide movement of a slat between stowed and deployed positions and a typical arrangement showing a cross-section through part of a wing 1 and a slat 2 in its stowed position is illustrated in FIG. 1. As can be seen from FIG. 1, the slat 2 is provided with an arcuate support arm or slat track 3, one end 4 of which is attached to the rear of the slat 2 and extends into the wing 1. To allow for wing bending and manufacturing tolerances, the end 4 of the slat track 3 is attached to the slat using spherical bearings and linkages (not shown). The slat track 3 penetrates wing spar 6 forming the wing structure. The slat track 3 defines an arc having an axis and is mounted within the wing so that it can rotate about that axis (in the direction indicated by arrows “A” and “B” in FIG. 1) to deploy and retract the slat 2 attached to one end of the slat track 3.
To drive the slat track 3 so as to deploy or retract the slat 2, a toothed slat track rack 7 having an arcuate shape corresponding to the arcuate shape of the slat track 3 is mounted within a recess 3a on the slat track 3 and a correspondingly toothed drive pinion 8 is in engagement with the teeth 7a on the slat track rack 7 so that when the drive pinion 8 rotates, the teeth 8a on the drive pinion 8 and the teeth 7a on the rack 7 cooperate to pivot or drive the slat rack 7 and the slat attached thereto, into a deployed position, i.e. in the direction of arrow “A” in FIG. 1. Typically, the slat track 3 rotates through an angle of 27 degrees between its fully stowed and fully deployed positions. Rotation of the pinion 8 in the opposite direction also drives the slat track 3, in the direction of arrow “B”, back into its stowed position, as shown in FIG. 1.
Although not shown in FIG. 1, each drive pinion 8 is geared to an outer shaft of a geared rotary actuator which extends concentrically over an inner input drive shaft that extends along the length of the wing within its leading edge, and which is driven by a slat deployment motor coupled to the inner input drive shaft at an inboard end of the wing. The inner input drive shaft is a common input drive shaft so that the slat deployment motor is operable to deploy all the slats of one wing together. The geared rotary actuator couples the inner input shaft to the outer output shaft so that the output shaft is driven by the inner input shaft. The rotary actuator also controls the speed of rotation of the output shaft relative to the input shaft so that the output shaft rotates approximately 200 to 300 times slower than the input shaft. A separate rotary actuator is associated with each drive pinion 8 and its accompanying slat track rack so there may be two or more geared rotary actuators per slat spaced along the length of the wing and extending concentrically over the input shaft.
The aforementioned assembly and method of deployment is described by way of example only and the detection system is applicable to the monitoring of the movement of any aero surfaces that are deployed together, irrespective of how that movement is achieved.
It is important to ensure that all the slats remain in alignment and deploy together and that, in the event of any misalignment such as skewing or asymmetry of one or more slats, continued operation of the actuation system is stopped and damage to the wing or the attachments between the wing and the moving surface is prevented. Skewing of a slat occurs when one of a number of slat deployment mechanisms associated with the same slat fails so that the slat deploys at an angle because it is still being driven away from the leading edge of the wing at an angle by the remaining slat deployment mechanism(s) associated with that slat. Asymmetry occurs when the slats on one wing are deployed at a different rate or extent to the slats on the other wing. Asymmetry or skewing of slats can be caused as a result of, for example, a defective rotary actuator, common drive shaft or coupling between the inner shaft and an outer shaft of a rotary actuator.
It is known to provide misalignment detection systems that rely on electo-mechanical technology and may include sensors and a lanyard passed through the aero bodies and connected to a switch at the end of the lanyard. However, such systems have to be able to accommodate misalignment caused by wing bending, thermal expansion and build tolerances and so must be inherently insensitive to ensure that false indications of misalignment are not given. This means that a significant misalignment may occur prior to it becoming detectable.
The present invention seeks to overcome or substantially alleviate the problems referred to above by providing a reliable and accurate system for detecting misalignment of a moving surface relative to other moving surfaces and for immediately stopping further deployment as soon as any misalignment is detected.